1. Technical Field
The present disclosure relates to an image forming device.
2. Description of the Related Art
As an exposure head which selectively exposes a photosensitive body and which is used in an image forming device such as a printer using an electrophotographic process, a configuration including a light-emitting element array and a microlens array is proposed as in Japanese Patent Application Laid-Open No. 2011-110762. As the light-emitting element, a Light Emitting Diode (LED) element, an organic Electro Luminescence (EL) element, or the like is used. In particular, when an organic EL element array is used as the exposure head, it is not necessary to arrange light-emitting elements with high accuracy as in the LED element array and the light-emitting elements can be monolithically formed on a substrate, so that it is possible to reduce the cost.
On the other hand, an image signal of each pixel in the light-emitting element array is determined by an area gray scale method such as a dither method and an error diffusion method in a gray scale presentation of a halftone image. Japanese Patent Application Laid-Open No. 2002-16802 proposes creating an image signal by a multi-value area gray scale method.
As a typical method of gray scale control of each light-emitting element, there is a pulse width modulation that controls the exposure time.
To perform the pulse width modulation, the number of thin film transistors (TFTs), which are elements of a peripheral circuit or a pixel circuit, increases, so that a decrease in yield and an increase in a substrate area according to an increase in the area of the entire area in which the TFTs are formed occur. Therefore, there is a problem that the cost increases.